Since a conventional coaxial connector comprises a thick inner conductor, it can hardly be installed on a small sized thin high frequency plate, and its performance characteristics drop drastically at a frequency over 6 GHz. A connector structure 10, wherein size of the inner conductor has been reduced gradually to allow the inner conductor to fit to a high frequency substrate, and diameter of the dielectric material has also been reduced to enable the impedance to be maintained at 50Ω, is show in FIG. 1.
The conventional connector 10 in FIG. 1 comprises an outer conductor 12, first dielectric 14 and an inner conductor 16. The connector 10 is electrically connected to a micro stripline (not shown in the drawing) of a microwave device 20 when it is installed within the microwave device 20. The inner conductor 16 of the connector 10 is electrically connected to an extendible pin 18. A second dielectric 30 made of fluorine-resin (Teflon) and inserted into a hole 22 of the microwave device 20 and the extendible pin 70 inserted into a hole 32 formed in the center of the second dielectric 30 are for impedance matching.
The inner conductor 16 of conventional connector 10 in FIG. 1 has a diameter reduced step-by-step toward the microwave device 20. Furthermore, size of dielectric 14 is also gradually changed to maintain an impedance of 50Ω. Thus, manufacturing of the dielectric 14 and of the inner conductor 16 becomes very troublesome; reflection property of the transmitted microwave signals is worsen due to the reflection of the microwave signals transmitted through the inner conductor, triggered by the varying conductor size; and a drastic drop of the performance characteristics occurs when the connector is connected to a transmission line. Actually, with the connector connected to a micro strip, a satisfactory performance cannot be expected at a frequency of 18 GHz or over. In addition, in the course of fixing the inner conductor by second dielectric, the thin inner conductor can be disconnected by heat of liquid form dielectric, and a correct line up of the extendible pin with the dielectric is also very difficult.
FIG. 2 shows another coaxial connector with conventional structure. Since main body of the connector 50 is made in detachable manner, this connector 50 is advantageous in recycling purposes or in exchanges at site. The connector 50 comprises an outer conductor 52, a dielectric 54, air 55, and an inner conductor 56. The connector 50 is connected mechanically to a microwave device through a connection means, e.g. bolt 57. An extendible pin 70 is inserted into the inner conductor 56 of the connector 50. Here, an extendible pin 70 is inserted into a bead form dielectric 80 made of melted glass ceramic with high dielectric ratio in order to compensate the difference in size of the extendible pin 70 from that of the inner conductor 56, and then, the dielectric 80 is inserted into the hole 65 of the microwave device 60 to yield a tightly sealed structure. In order to make a sealing construction, the hole 65 of the microwave device 60 has a two stage structure, e.g. the hole 65 consists of a first insertion stage with a diameter of 0.7 mm corresponding to the thin diameter of the inner conductor 56 to maintain an impedance of 50Ω and a second insertion stage corresponding to the diameter of the extendible pin 70. The extendible pin 70 is electrically connected to the micro strip 62 of the microwave device 60 after it has passed through the second insertion stage.
However, in order to enable a connection with the conventional connector in FIG. 2, a two stage drilling of the microwave device is required, which is not advantageous. Since diameters and depths of the insertion holes of a microwave device are very sensitive to the overall performance characteristics of the connection structure, the insertion holes shall preferable be made as simple as possible. Moreover, manufacturing of the glass ceramic for the sealing structure is troublesome and requires a high cost.